1. Field of the Invention
The present invention relates to an ink jet recording apparatus which discharges ink from a recording head on the basis of image information to record an image, and specifically relates to the ink jet recording apparatus provided with an ink collecting mechanism for collecting ink drained from a recovery unit.
2. Description of the Related Art
A recording apparatus is used for a recording apparatus having a function such as a printer, a copying machine and a facsimile; multifunction equipment including a computer and a word processor; or output equipment of a workstation. The recording apparatus is composed so as to record an image on a recording medium such as paper and a plastic sheet, on the basis of image information. The recording apparatus can be classified into an ink jet printing type, a wire dot printing type, a hot printing type, a thermal printing type and a laser beam printing type, according to a recording system. A recording apparatus can be also classified into a serial type and a line type according to a scanning system. The serial type recording apparatus records an image by combining horizontal scanning which moves a recording head along a recording medium, and vertical scanning which feeds the recording medium. The line type recording apparatus records the image only by vertical scanning in a conveying direction of the recording medium, while recording information corresponding to one line by one operation with the use of a recording head stretching in the cross direction of the recording medium.
An ink jet printing type recording apparatus (ink jet recording apparatus) discharges ink from an ink jet recording head to a recording medium on the basis of image information to record an image. The ink jet recording apparatus has advantages such as a low noise level, a low running cost and easiness of being miniaturized and of being colored, and accordingly is widely applied to a printer, a facsimile and a copying machine. The recording head which is used as a recording unit in an ink jet recording apparatus is provided with a discharge port (in general, an end opening of a nozzle) for discharging ink. The ink jet recording apparatus drives the recording head and makes it discharge an ink droplet from the discharge port in response to a discharge signal based on recorded data sent from a host device such as a personal computer in general. The discharge port (or the nozzle) has a diameter of several tens of micrometers for instance, when being circular, and is further refined and densified as a picture quality of the recording image becomes higher in recent years. Such a recording head is required, for instance, to print a denser black character and the like, print colors, print a finer image (higher resolution) and have improved water resistance, as the quality of the recording image becomes higher in recent years.
In general, a serial type of the ink jet recording apparatus mounts a recording head on a carriage, and records an image by making the recording head discharge ink according to the reciprocating movement of the carriage and form a dot on a recording medium. An example of the recording head in the serial type of the ink jet recording apparatus, which inexpensively satisfies the requirement for enhancing the quality of a recorded image, includes the one having a configuration shown in FIG. 3, which will be described later as an embodiment. Specifically, the recording head 3 configures a discharge port array 13 for black ink, a discharge port array 14 for yellow ink, a discharge port array 15 for magenta ink and a discharge port array 16 for cyan ink on a common discharge face 17 of the recording head 3 in parallel to the scanning direction of the recording head. In the above configuration, discharge ports in each discharge port array are arranged at a pitch corresponding to 600 dpi (dot per inch) along with the tendency of high accuracy, and further at a pitch corresponding to even 1200 dpi. The pitches between the respective discharge port arrays are also decreased so as to miniaturize the recording head and consequently the apparatus.
Incidentally, there is a recording head capable of coping with high quality recording, which employs inks that cause a chemical reaction, for instance, between black ink and other color ink and insolubilize a dye or the like by the chemical reaction, in order to improve water resistance and prevent blur between colors. Specifically, for instance, the black ink has a cationic property and the other color ink has an anionic property. In addition, Japanese Patent Application Laid-Open No. 2000-063719 discloses the ink which employs an ink composition using a pigment as a coloring material and a reaction liquid for making the coloring material in the ink composition unstable, makes the coloring material coagulate by using the reaction between the two liquids, and inhibits the ink from causing the blur or color mixture (bleeding) on plain paper. In addition, Japanese Patent Application Laid-Open No. 2000-198955 discloses the ink and ink set which employs a pigment as a coloring material, further adds a particular salt into the ink, and inhibits the bleeding.
In recent years, ink containing a pigment component as black ink has been commonly used so as to improve the quality of a black character used in a text document or the like.
Incidentally, an ink jet recording apparatus records an image by discharging ink from a fine discharge port, so that the state of the ink in the vicinity of the discharge port tends to be affected by an environment factor such as humidity. For instance, the ink can be solidified and fixed by drying. Then, ink cannot be discharged at regular timing, which deteriorates image quality. For this reason, this type of the ink jet recording apparatus is provided with a cap which closely contacts a discharge face (face having discharge ports arrayed thereon) of a recording head to seal the discharge port (to intercept it from outer air). In the case of a serial type of a recording apparatus, the cap is arranged at a predetermined position (for instance, a home position of the recording head) outside the recording area. Thus, the recording apparatus prevents the ink in the discharge port (in a nozzle) from thickening and being solidified through evaporating and being dried while the recording apparatus is not printing.
On the other hand, an ink jet recording apparatus may cause clogging in a discharge port. In order to prevent the clogging, ink is sucked (drained) from the discharge port through a cap by using a negative pressure source such as a sucking pump, which is a sucking recovery operation. In other words, the ink is forcefully sucked from the discharge port, by the operation of connecting the sucking pump to the cap and operating the sucking pump in a state of being capped to form a negative pressure in the cap. The operation replaces the ink in the discharge port with a new ink, and consequently can prevent or resolve (recovered) the clogging in the discharge port. A usable pump for generating the negative pressure includes a piston-cylinder-type pump or a tube pump, for instance. The piston-cylinder-type pump uses the movement of the piston in a cylinder. The tube pump generates the negative pressure in the tube by squeezing the elastic tube connected to the cap with a roller and using the returning force of the elastic tube.
An ink jet recording apparatus also wipes a discharge face with a wiper such as a rubber blade in order to remove a foreign material such as ink and dirt depositing on the discharge face. The ink jet recording apparatus also replaces the ink in the discharge port with a flesh ink, by discharging an ink that is not directed at recording to an ink sump from the discharge port, which is a preliminary discharge operation. The ink jet recording apparatus keeps or recovers an ink-discharging performance of a recording head by the above described sucking operation, wiping operation and preliminary discharge operation, which is recovery treatment.
Various researches and developments have proceeded on properties of ink in order to respond to the requirement of high-resolution recording. A first developed ink for inhibiting the ink from causing blur and color mixture (bleeding) on a recording medium of plain paper or the like is an ink showing such properties as the black ink and the color ink for forming a recording image react with each other, and are solidified or thickened. Such a type of ink may be thickened and solidified in a tube or a waste ink sump while the above described recovery operation is carried out, and may hinder the recovery operation from being normally carried out. For this reason, as disclosed in Japanese Patent Application Laid-Open No. 2002-225312 for instance, a recovery unit is separately placed in each of a discharge portion (discharge port) for black ink and a discharge portion (discharge port) for color ink so that the inks are not be thickened and solidified in a cap or the recovery tube.
The ink (waste ink), which has been drained by the above described recovery treatment is introduced into an ink absorbing member placed in a main body of a recording apparatus through a tube placed in a downstream side of a sucking pump, is absorbed by the ink absorbing member and is collected. On the other hand, there is a method for achieving a picture of high quality when the picture is recorded on plain paper, by promoting the coagulation of color materials in ink on the paper surface. The method also enhances coagulating properties of the ink drained during the recovery treatment, namely, a waste ink which is not used in recording. Accordingly, it is important for the ink absorbing member for collecting the waste ink through the recovery treatment to efficiently absorb the ink having the rapidly coagulating properties. As for a conventional structure for storing the waste ink, for instance, Japanese Patent Application Laid-Open No. 2000-127439 discloses a waste ink tank that accommodates the ink absorbing member which has a recess extending to a position including a waste ink inlet formed therein. In addition, Japanese Patent Application Laid-Open No. 2001-105626 discloses a waste ink tank that accommodates an ink absorbing member having a through-hole through which the waste ink is drained dropwise, and having a cut channel radially formed from the through-hole.
However, a structure described in Japanese Patent Application Laid-Open No. 2002-225312 needs to separately install a capping unit in each of discharge port arrays for black ink and color ink, needs to upsize a recording head, and consequently increases a cost for manufacturing an ink jet recording apparatus. As a method for solving the problem that the recording head needs to be upsized, a method is conceived which prevents the above described thickened substance from forming by using inks of black pigment ink and color dye ink that do not react with each other. Such a method enables the pigment ink and the dye ink to be sucked and restored while preventing the mixture of both inks from being thickened, precipitating or being solidified, even when both of the inks are simultaneously and preliminarily discharged from one discharge face having the discharge port array for the pigment ink and the discharge port array for the dye ink arranged therein. However, such a method causes a technical problem that the black ink and the color ink produce bleeding (blur or color mixture) between them when an image is recorded on plain paper.
The present inventors made an extensive investigate on the improvement of ink, while aiming at the further improvement of image performance such as image density and the capability of inhibiting bleeding, and as a result, it has been elucidated that the ink which instantly lowers its dispersion stability and increases viscosity due to the evaporation of water shows higher image performance as well. The above type of ink causes viscosity increase (viscosity rise-up) not by a rapid coagulation reaction such as an electrostatic neutralizing reaction occurring between an anion and a cation, but by a reduction of a water in an ink liquid, and accordingly shows a large effect only in the latter case. Accordingly, a recording head even having a discharge port array for a pigment ink and a discharge port array for a dye ink arranged together thereon can suck a mixed ink containing a pigment and a dye without causing the thickening, precipitation or solidification of the mixed ink, even by using a common sucking unit, and can restore itself. In other words, the mixed ink does not lower its dispersion stability so long as the mixed ink is not dried due to the evaporation or diffusion of water, accordingly is kept at low viscosity and does not cause any problem in being sucked and restored. However, the ink (waste ink) which instantly decreases the dispersion stability due to the evaporation of water has lower absorbance by the ink absorbing member than the conventional ink. Accordingly, there was a case where the conventional waste-ink absorbing member could not sufficiently absorb the waste ink.
Japanese Patent Application Laid-Open Nos. 2002-225312 and 2000-127439 disclose that the ink absorbing member can inhibit waste ink from evaporating in the vicinity of a waste ink introduction part and can avoid the waste ink from losing flowability by forming a recess or a cut channel in the ink absorbing member, which extends from a position including the waste ink introduction part. However, when the ink has properties of instantly decreasing dispersion stability due to the evaporation of water, a pigment in the ink is solidified and fixed at a position at which the ink is drained dropwise into a waste ink tank. In other words, when the waste ink contacts a waste-ink absorbing member before the waste ink decreases flowability, a pigment in the waste ink precipitates and is fixed at the contact position. As a result of this, there was a case where the waste ink drained dropwise at the position deposited on a fixed matter as a core and finally blocked the flow of the ink to the recess or the cut channel. As a result of this, there was a case where the waste ink overflowed from the vicinity of the waste-ink introduction site before the whole recess or cut channel was used to the maximum, and the whole waste-ink absorbing member could not be effectively used.